In this paper, barium titanate nanoparticles (BaTiO 3 , BT) were incorporated into the polyurethane (TPU) matrix to prepare dielectric elastomer composites.Then, the composites were thermal treated to improve the interfacial compatibility between TPU and BT, enhance the interface polarization, and improve the dielectric properties. The results showed that the dielectric constant of the composites after thermal treatment at 150 C reached to 7.3 at 1 kHz, the elongation at break remained 1934%, and the elastic modulus (Y) dropped to 4.4 MPa. In addition, the discharge energy density reached 73 mJ/cm 3 under an electric field of 300 kV/cm, and charge-discharge energy conversion efficiency was up to 84%. More importantly, the electrically actuated displacement of 2.61 mm at electric field of 160 kV/cm was 1.7 times greater than that of untreated composites. The composites worked stably under the action of the circulating electric field. This study provided a new strategy for obtaining highperformance dielectric elastomer actuators, which were expected to be applied to biomimetic robots, human skin, or dielectric energy storage devices.

Here, we demonstrate the design and application of a multifunctional piezoelectric composite nanofiber membrane. In this study, the most widely used electrospinning method, by adding a small amount of 1-allyl-3-butylimidazolium tetrafluoroborate ionic liquids and ferric chloride hexahydrate (FeCl 3 Á6H 2 O) to regulate the structure and properties of polyacrylonitrile (PAN), the mechanical properties, piezoelectric properties, dielectric properties, and ferroelectric properties of composite nanofibers were improved. The results show that the piezoelectric properties of PAN composite fibers are greatly improved under the action of dual fillers. At 10 3 Hz, the dielectric constant of the PAN composite fiber is as high as 8.24, which is three times that of the pure PAN fiber. The sensor made from the composite nanofibers exhibits excellent sensitivity and high saturation polarization. At low pressure (<1 kPa), the sensitivity of the composite fiber is as high as 0.51 kPa. When we tap the sensor with our finger, the PAN composite fiber produces high piezoelectric output (5.7 V). The results show that the composite nanofibers have great potential in energy storage devices and flexible piezoelectric sensors, among other fields.

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Aiming at the multisize effect of mining in steeply inclined extrathick coal seam, taking the fully mechanized top-coal caving mining in B3+6 coal seam +425 level in the south of Wudong coal mine as the background, this paper studies the mining stress evolution law under the influence of advancing speed, analyzes the mechanical characteristics of coal samples under the mining action of steeply inclined extrathick coal seam, and completes the multisize effect study of mining in steeply inclined extrathick coal seam. The results show that the stress change theory of fully mechanized top-coal caving mining in steeply inclined seam is deduced, and the loading and unloading stress of fully mechanized top-coal caving mining is positively correlated with the advancing speed of the working face. The numerical simulation experiment shows that the ideal advancing condition increases with the advancing speed of the working face, and the cyclic loading and unloading amplitude under the mining stress path increases, the cyclic times decrease, the main influence area increases, and the acting time decreases. The peak value of mining stress, the width of the plastic zone, and its elastic energy under high-speed propulsion are obviously larger. A method of mechanical behavior analysis of coal samples is proposed, which takes the mining stress path of the numerical simulation experiment as the indoor scale loading and unloading stress path of coal samples. The average compressive strength of coal samples under the mining stress path increases with the advancing speed of the working face, and the damage degree of coal samples increases with the advancing speed of different stress paths. The input strain energy of coal cyclic loading and unloading increases with the increase in the advancing speed of the stress path. The input strain energy of the coal sample has obvious linear relationship with the advancing speed of different paths. The research results can be used for reference in the study of multisize effect of mining impact of advancing speed.

The development of flexible materials with higher piezoelectric properties and electrostrictive response is of great significance in many applications such as wearable functional devices, flexible sensors, and actuators. In this study, we report an efficient fabrication strategy to construct a highly sensitive (0.72 kPa –1 ), red light-emitting flexible pressure sensor using electrospun Eu 3+ -doped polyvinylidene fluoride–hexafluoropropylene/graphene oxide composite nanofibers using a layer-by-layer technology. The high β-phase concentration (96.3%) was achieved from the Eu 3+ -doped P(VDF-HFP)/GO nanofibers, leading to a high piezoelectricity of the composite nanofibers. We observed that a pressure sensor is enabled to generate an output voltage of 4.5 V. Furthermore, Eu 3+ -doped P(VDF-HFP)/GO composite nanofiber-based pressure sensors can also be used as an actuator as it has a good electrostrictive effect. At the same time, the nanofiber membrane has excellent ferroelectric properties and good fluorescence properties. These results indicate that this material has great application potential in the fields of photoluminescent fabrics, flexible sensors, soft actuators, and energy storage devices.